united-states
The general rule is that contracts may be reformed to reflect the intent of the parties if the evidence shows that what was committed to writing was contrary to the intent of the parties. This general rule is an exception to the rule that parties are conclusively presumed to have read and agreed to all terms of a duly executed written contract whether they actually did so or not.
In the case of a written contract, the main rule that interferes with the application of this general rule allowing contracts to be reformed to reflect the intent of the parties is called the "parol evidence rule". The parol evidence rule provides that an unambiguous written contract that is intended to be a full statement of the rights of the parties (i.e. to be the "entire agreement of the parties") cannot be modified or colored based upon "extrinsic evidence" regarding the negotiations leading up to the execution of the written contract.
As the first link explains:
In contract disputes, parol evidence is any agreement that is not
contained within the written contract. Under the parol evidence rule,
these agreements made outside of the contract are inadmissible in
court unless there is evidence of fraud, duress, or a mutual
mistake. The rationale behind the rule is to deter untruthful
attacks on contracts.
The parol evidence rule bars extrinsic evidence, including prior or
contemporaneous oral agreements and prior or contemporaneous written
agreements, that contradict or create a variation of a term in writing
that the parties intended to be completely integrated. In other words,
any information leading up to or during a contract that is not
included in writing is considered inadmissible evidence and is
excluded from the jury. The jury will therefore only look at the
writing within the document itself to decide a contract dispute.
Furthermore, interpretation of a written contract is a question of law for the judge and not the jury to decide. See, e.g., this Arkansas Model Civil Jury Instruction and the cases cited therein in support of it.
So, if the valid execution of a written contract is undisputed (as it usually is when parties used lawyer drafted business contracts), usually the jury's job is to decide if the duties established by the contract, as interpreted by the judge without extrinsic evidence, were breached by the actions of the parties, and if so, what damages were caused by the breach under a definition of contract damages provided by the judge.
When the party bringing the lawsuit is suing for non-payment when it was due under the contract (which is the predominant type of breach of contract lawsuit arising from a breach of a written agreement), however, the amount of the damages owed if there was a breach of the contract usually leaves the jury with no discretion regarding the amount of damages owed if the contract was breached by the defendant's failure to pay, and the amount owed to the person bringing the contract claim if the amounts due were not paid as agreed. Usually, the payment history can be established with third-party banking records. So, the jury is left to decide merely whether there was any legally recognized justification for the non-payment (if the non-payment is established with evidence at trial).
The fact that a jury has so little discretion in cases involved alleged breaches of written contracts whose execution is undisputed is one of the reasons that 75% or more of high stakes contract disputes in courts of general jurisdiction are resolved in bench trials before a judge rather than by a jury jury, even when the contract does not itself waive a right to a trial by jury.
When one of the named parties to a written contract is the name of someone other than the person mutually intended by the parties forming the contract, then this is a mutual mistake. As a result, the contract can be reformed by the judge to state the name of the intended party to the contract under the principles of equity jurisprudence (if the party seeking the reformation established the mutual mistake with evidence meeting the applicable burden of proof), before the reformed contract whose breach is alleged is submitted to a judge or jury on the merits to see if the acts of the defendant breached the reformed contract terms.
However, if there is a bona fide dispute regarding who was agreeing to the contract, and not just a mutual mistake when both parties shared an understanding regarding who the correct party to the contract was, the contract could be found to be void and unenforceable because the parties did not reach a "meeting of the minds" regarding who was entering into a contract with whom.
This kind of ambiguity could arise, for example, when the name of the party in a contract is stated in an ambiguous way. For example, I had a recent case that described the party obligated on a promissory note as:
[Entity Name], i.e. [individual name of the owner of the entity]
This description is ambiguous and contradictory on its face.
The party who drafted this promissory note language without a lawyer thought that this made both the entity and the individual who owned the entity liable to repay the promissory note.
But the individual who owned the entity argued that only the entity (which had no material assets at the time that the lawsuit was filed) had liability on the promissory note.
In the end, the question was not resolved by the court and the promissory note creditor conceded the issue, in part, because the individual owner of the entity didn't have many significant assets either.
Differences between jurisdictions
The burden of proof to reform a contract varies
The burden of proof that a party must meet to establish that there was a mutual mistake authorizing the reform of the contract varies from one jurisdiction to another. Some U.S. states and other common law jurisdictions follow the general rule in civil cases that claims must be proved by a preponderance of the evidence.
Other U.S. states and common law jurisdictions apply a higher burden of proof to claims that seek to circumvent the parol evidence rule by reforming the contract and required that the basis for extraordinary remedy of reforming a written contract (whose due execution is undisputed) to reflect the intent of the parties must be shown by clear and convincing evidence or some similar burden of proof, rather than the usual more likely than not preponderance of the evidence standard that usually applies in civil lawsuits. (I couldn't tell you which burden of proof is the majority rule.)
Some non-common law jurisdictions do not follow the parol evidence rule
The parol evidence rule has its roots in the English common law of contracts and is shared by almost all common law legal jurisdictions internationally.
But there are notable examples of legal jurisdictions that are not common law legal jurisdictions dispensing with the parol evidence rule entirely, in jurisdictions that have civil law legal systems, based upon the legal systems of continental Europe like France, Germany, Portugal and Spain, and in jurisdictions that have hybrid legal systems that has some features that are more like common law jurisdictions, and other features that are more like civil law jurisdictions.
Legal scholarship regarding the parol evidence rule often emphasizes the fact that despite the centrality of the parol evidence rule in a large share of cases governed by the common law of contract actually experience very few difficulties in justly and efficiently adjudicating contract cases, notwithstanding the parade of horribles that the parol evidence rule is supposed to avoid.
israel
For example, the courts of Israel, which use a hybrid of civil law and common law jurisprudence, do not have a parol evidence rule and allow the admission of any potentially relevant evidence regarding the intent of the parties to a contract to be introduced in court. Israel allows this evidence to be admitted and considered by the judges deciding the case, even if the written contract is unambiguous, is in writing, and purports to be the entire agreement of the parties, without a showing of fraud, duress, or mutual mistake. See, e.g., this law review article from the year 2008, which states:
Israeli courts apply a model of “purposive interpretation” to all
legal interactions and texts. The role of contract interpretation is
to reconstruct the agreement in light of the manifested common purpose
of the parties at the time of formation. Thus, Israeli courts do not
apply the parol evidence rule, and allow interpretative evidence
regarding context, circumstances, and parties’ behavior before,
during, and sometimes even after formation. Nor do courts, in general,
use other exclusionary devices that may frustrate true understanding
of the agreement between the parties. Courts may resort to the
“rational of the deal” as an interpretative yardstick. Customs,
courses of conduct, prior agreements and lex mercatoria may be
brought in evidence of the parties’ purported agreement and sometimes
form interpretative presumptions. Good faith is applied as an
interpretative principle as well; thus when reconstructing the
parties’ purposes, a party may not benefit from having failed to
disclose information that under the good faith requirement it should
have disclosed.
In practice, Israel's approach generally does not give rise to the problems that the conventional wisdom justifications for the parol evidence rule claim that omitting it as a legal principle would cause.